Cyclic carbonates are used as organic solvents, agents for processing synthetic fibers, raw materials for medicaments, cosmetic additives and electrolyte solvents for lithium batteries, and are also utilized for the synthesis of alkylene glycols and dialkyl carbonates, and the like (Patent Literature 1), and thus are one of important compounds that are used in a wide variety of applications.
Conventionally, the cyclic carbonates have been synthesized by reacting an epoxide and carbon dioxide in the presence of a homogeneous system catalyst under a suitable pressurized condition. As such homogeneous system catalyst, halides of alkali metals and onium salts such as quaternary ammonium salts have been conventionally known (Patent Literature 2), and are industrially used.
However, in the case when such homogeneous system catalyst is used, a separation operation to separate the reaction mixture and catalyst by distillation, or the like is generally required, and thus the production steps become complex, and there are problems of the decomposition of the catalyst during the separation step and the generation of by-products.
Therefore, for the purpose of simplifying the catalyst separation process, a heterogenous catalyst in which quaternary phosphonium each having a halide ion as a counterion are immobilized on a support such as a silica gel, and a heterogenous catalyst in which an alkali metal element or an alkaline earth metal element has been formed into a composite oxide with phosphorus, silica or the like, have been suggested (Patent Literatures 3 to 5).